U.S. Pat. No. 7,940,137 B2 discloses a method for controlling loop gain of a crystal oscillator circuit using a bias current. A bias current which is employed as a parameter for controlling the drive level of the oscillator is set to a high value at start-up and then reduced stepwise until the amplitude of the oscillator signal falls below a threshold. This requires a rather complicated circuit with expensive high-quality components for monitoring the amplitude and controlling the bias current via a feedback loop involving rectifying and analog to digital (A/D)-converting the output signal and digital to analog (D/A)-converting a digital signal which controls the bias current. The rather involved signal processing also causes elevated levels of power consumption.